AbstractBackgroundMethodsResultsConclusionsIntroductionMethodsEnvironmental Specimen CollectionHuman Subjects and SettingHair CollectionMercury AnalysisAnalysis for Persistent Organic PollutantsStatistical AnalysisResultsDiscussionConclusionsList of AbbreviationsAcknowledgementsAuthor detailsAuthors' contributionsCompeting interestsReferencesRESEARC H Open AccessMethylmercury exposure in a subsistencefishing community in Lake Chapala, Mexico:an ecological approachLeonardo Trasande1,2, Juanita E Cortes3, Philip J Landrigan1,2, Mary I Abercrombie5, Richard F Bopp5,Enrique Cifuentes1,4*AbstractBackground: Elevated concentrations of mercury have been documented in fish in Lake Chapala in centralMexico, an area that is home to a large subsistence fishing community. However, neither the extent of humanmercury exposure nor its sources and routes have been elucidated.Methods: Total mercury concentrati ons were measured in samples of fish from Lake Chapala; in sections ofsediment cores from the delta of Rio Lerma, the major tributary to the lake; and in a series of suspended-particlesamples collected at sites from the mouth of the Lerma to mid-Lake. A cross-sectional survey of 92 womenranging in age from 18-45 years was conducted in three communities along the Lake to investigate therelationship between fish consumption and hair me rcury concentrations among women of child-bearing age.Results: Highest conce ntrations of mercury in fish samples were found in carp (mean 0.87 ppm). Sediment datasuggest a pattern of moderate ongoing contamination. Analyses of particles filtered from the water columnshowed highest concentrations of mercury near the mouth of the Lerma. In the human study, 27.2% of womenhad >1 ppm hair mercury. On multivariable analysis, carp consumption and consumption of fish purchased orcaptured from Lak e Chapala were both associated with significantly higher mean hair mercury concentrations.Conclusions: Our preliminary dat a indicate that, despite a moderate level of contamination in recent sedimentsand suspended particulate matter, carp in Lake Chapala contain mercury concentrations of concern for local fishconsumers. Consumption of carp appears to contribute significa ntly to body burden in this pop ulation. Furtherstudies of the consequences of prenatal exposure for child neurodevelopment are being initiated.IntroductionMercury is an ubiquitous environmental toxin. It existsin three general forms with different bioavailability andtoxicity profiles – the metallic element, inorganic mer-cury and organ ic mercury [1 ]. While coal -fired powerplants and chloralkali plants are the leading pointsources of mercury emissions in man y industrializedcountries [2,3], releases associated with amalgamation ofprecious metals may dominate in regions practicing arti-sanal mining of gold a nd silver [4]. Emissions from vol-canoes are an important natural source and forest fires,often associated with clearing land for agriculture, canbe significant [5,6] with disproportionate impacts inareas of current and recent deforestation [7-9].Mercury is released from combustion sources in bothelemental and inorganic forms. In the atmosphere, ele-mental me rcury is converted to inorganic ("reactive”)forms that eventually deposit into soil and water. Once innatural water systems, via direct deposition or terrestrialrunoff, a portion of the mercury can be transformed toan organic form, methylmercury. The microbially-mediated process occurs both in sediments and in thewater column [10]. Methylmercury is a potent neurotoxi-cant, especially to the developing brain [11,12]. It b io-magnifies in aquatic food chains where “nearly 100% ofthe mercury that bioaccumulates in upper-trophic-levelfish (predator) tissue i s methylmercury” [13]. Highest* Correspondence: [email protected] of Community and Preventive Medicine, Mount Sinai School ofMedicine, 1 Gustave L Levy Place, Box 1057, New York, NY 10029, USATrasande et al. Environmental Health 2010, 9:1http://www.ehjournal.net/content/9/1/1© 2010 Trasande et al; li censee BioMed Central Ltd. This is an Open Ac cess article distributed under the term s of the CreativeCommons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andreproduction in any medium, provided the original work is properly cited.concentrations are generally found in predatory fish atthe top of the food chain - swordfish, tuna, king mackereland shark in marine systems [14-17]; and black bass, wal-leye, and northern pike in freshwater systems [18]. Con-sumption of contaminated fish is the most importantroute of human exposure to methylmercury [19]. Studiesin New Zealand, [20,21] the Faroe Islands, [11,22] andthe Seychelles Islands [23] have followed cohorts to assessthe impact of fetal methylmercury exposure. In a reviewof these three studies, the National Academy of Sciences(NAS) found strong evidence for neurotoxicity, even atrelatively low e xposure [24]. Since the NAS report, anAmerican cohort has associa ted elevated hair merc uryconcentrations with decreases in cognition among infants.The association persisted even when controlled formaternal fish consumption [12].Lake Chapala is the largest watershed in Mexico (Figure1; Table S-3 in Ad ditional file 1) and it collects water forone-eighth of all the irrigated land in Mexico. Some300,000 people live in communities around Lake Chapala,and to varying degrees rely upon fish caught or purchasedfrom the lake for their subsistence. Economic activitieshave created increasing pressure on the whole ecosys temprompting representat ives from the concerned fishingcommunities to solicit an assessment of the health riskposed by industrial sewage discharges and agriculturalpractices (e.g., slash and burn). Previous reports of fishmercury concentrations (0.05-1.84 μg/g wet weight), someexceeding international guidelines (0.5-1.0 ppm), haveraised serious concerns about health risks to families whorely on fish from the lake for their subsistence [25,26].In response to inc reasing community concerns aboutpotential health risks, an environmental samplingappr oach was used to study pathways of methylmercuryexposure in this subsistence fishing population. Mercurycontamination was assessed in carp, whitefish and tilapiafrom Lake Chapala collected in March 2007, and con-tamination with polychlorinated biphenyls and persistentpesticides was explored through analysis of the fish